Book Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1895 edition. Excerpt: ...surface, or wave, noticeable above a revolving screw. In an account of the speed trial of the triple-screw U. S. S. "Columbia" the following is related: "The most noticeable feature of the trial of the ship itself was the remarkable absence of all wave. The triangular foaming cataract at the stern formed with its apex about ten feet from the ship and then subsided in height as it spread in width, until it disappeared fifty feet further aft into a series of gentle waves, similar to those which are seen in the wake of a stern-wheel steamboat." In some instances where the screws revolve very rapidly, and the form of the after part of the vessel and position of the screws are favorable for it, the elevation resulting from the discharge of screws is excessive. In the case of the torpedo boat " Cushing " it attains a height of three or four feet above the normal surface. When the immersion of the screw is sufficient, there may be little or no noticeable elevation of surface over it, because the discharged water will be widely dispersed and equilibrium will be restored before the surface can be affected to a sensible degree. In Trans. Inst. Nav. Arch., 1879, Mr. Griffiths recites the results of experiments he was allowed to make on H. M. steam pinnace No. 22 in 1875 by measuring, with apparatus specially constructed for the purpose, the rate at which the water flowed through the screw disk while the boat was being towed. These experiments showed that over the bottom half the water was little interfered with, but at the top half of the disk the water was dragged with the boat to a certain extent, and only flowed through the screw at about half the speed of the boat's progress. When a ship is being driven by a screw...